title: Meta-analysis of the association between preterm delivery and intelligence.
abstract: BACKGROUND
  An increasing proportion of infants are born preterm, and their survival has improved. Therefore, their long-term sequelae are of increasing public health importance.
  
  
  METHODS
  We conducted a systematic review covering a 30 year period (1980-2009). A random effects meta-analysis provided a pooled estimate of the difference in IQ score between individuals born preterm and term. Small-study bias was examined using a funnel plot and Egger's test, and meta-regression was used to investigate possible causes of heterogeneity. Cumulative meta-analysis was used to determine if the magnitude of the association had changed over time.
  
  
  RESULTS
  The 27 eligible studies covered 7044 individuals; 3504 (50%) delivered preterm and 3540 (50%) at term. They provided 37 estimates of difference in IQ. All demonstrated a reduced IQ among those delivered preterm and all but four reached statistical significance. Overall, IQ score was 11.94 (95% CI: 10.47-13.42, P < 0.001) points lower among children born preterm. There was moderate heterogeneity (overall I(2) 74.2%, P < 0.001), but no significant small-study bias (P = 0.524). The association between preterm delivery and IQ did not change significantly over time. There was a statistically significant, linear association across the gestational age range (adjusted coefficient: -0.91, 95% CI: -1.64, -0.17, P = 0.018).
  
  
  CONCLUSIONS
  There is a strong and consistent body of evidence suggesting an association between preterm delivery and reduced IQ, with evidence of a dose-response relationship with gestational age.
authors.affiliation: Centre for Population Health Sciences,  University of Glasgow, Glasgow G12 8RZ,  UK.
authors.forename: C O
authors.initials: CO
authors.lastname: Kerr-Wilson
authors.forename: D F
authors.initials: DF
authors.lastname: Mackay
authors.forename: G C S
authors.initials: GC
authors.lastname: Smith
authors.forename: J P
authors.initials: JP
authors.lastname: Pell
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007360:Intelligence / Q000502:physiology*; D007361:Intelligence Tests; D008297:Male; D011247:Pregnancy; D047928:Premature Birth